Nuclear‐Magnetic‐Resonance with ¹³C and ³¹P and Circular‐Dichroism Studies of a Ternary Complex of Spermine, Cu²⁺ and AMP

Abstract

The formation of a ternary complex using cupric ions, basic amines of biological significance, and nucleotides was examined employing high-resolution nuclear magnetic resonance (NMR) with I3C and 31P and circular dichroism. The reaction of Cu2+ with each ligand was studied separately and as the ternary complex. From I3C-NMR data the assignment of the respective carbon atoms adjacent to a copper-binding atom was clearly shown. It is intriguing to note that even in such a ternary complex the N-7 of the purine ring, as well as the phosphate residue (measured by 31P-NMR spectroscopy) provide the preferred binding sites for the cupric ion. Marked interactions of the chelated cupric ion with the ribose moiety in the ternary complex were deduced from circular dichroic measurements. No such reactivity was seen when dAMP was employed. The existence of a ternary Cu . AMP . amine complex opens a number of new aspects regarding the reactivity of metal ions in the biochemistry of nucleic acids.The involvement of metal ions in the biosynthesis and catabolism of nucleic acids has been intensively studied [l -71. The chemical and structural properties of transition metal complexes with polynucleotides and their monomeric constituents have been investigated and substantial structural evidence collected in recent years [for reviews see [l -31). Regarding the metal . nucleotide complexes, it has been demonstrated that metal binding can occur with the bases, the phosphate residues and possibly with the ribose moiety. These conclusions were drawn from X-ray diffraction studies and a large number of different spectroscopic measurements including electronic spectra, paramagnetic resonance studies, chiroptical measurements and recently X-ray photoelectron spectroscopy [8].Due to the rather low thermodynamic stability of metal . nucleotide complexes, it has proved impossible to isolate such complexes from biological tissues. In this context, the question arises whether or not those metal chelates really play a functional role in bioAbbreviations. NMR, nuclear magnetic resonance; CD,logical systems in view of the fact that other more avid chelators are also present. The metal ion concentration required to form binary complexes of suitable stability is in the millimolar range with the consequence that many dissociated metal ions would lead to harmful reactions in the different metabolic pathways. Nevertheless, the essential function of many metal ions, including transition elements, in the biochemistry of nucleic acids remains a solid fact. The simple picture of metal . nucleotide complexes, however, needs a thorough revision. The monomeric and polymeric nucleotides are found quite frequently associated with proteins. Metals in metalloproteins are bound firmly enough to survive isolation from biological material. Thus, we propose the existence of ternary complexes involving all three components, i.e. proteins, nucleotides and metal ions, which might be expected to be less vulnerable to breakdown than binary chelates [7,9].An approach in t...

Noncovalent interactions and coordination reactions in the systems consisting of copper(II) ions, aspartic acid and diamines

“…The results were also carefully verified with the equilibrium data and electronic spectra observations. A similar problem has been earlier discussed for other systems with Cu(II) ions [22,42,43].…”

The effect of spermine concentration on the solution structure of complexes formed in copper(II)/adenosine 5′-triphosphate/phosphoserine system

“…1) are: the endocyclic nitrogen atoms N(1) or N(7) of adenine ring and the phosphate groups in ATP, the carboxyl, phosphate and amine groups in Ser-P and two terminal amine groups as well as two secondary amine groups in Spm [38][39][40][41][42]. These groups are also potential sites of noncovalent interactions as we have recently found in many similar systems [43][44][45]. Model selection (including stoichiometric composition and stability constants) was done using potentiometric method.…”

Interaction centres of pyrimidine nucleotides: Cytidine-5′-diphosphate (CDP) and cytidine-5′-triphosphate (CTP) in their reactions with tetramines and Cu(II) ions

“…Significant changes in the chemical shifts were only observed in the pH ranges in which the occurrence of the complexes was deduced on the basis of the potentiometric measurements. The NMR method has been earlier applied in order to study similar systems [31,40,50,55,56].…”